Field
Embodiments of the disclosure relate generally to the field of lightning protection of non-metallic structures and more particularly to lightning protection of aerospace structures fabricated from carbon fiber reinforced plastic (CFRP) composite systems.
Background
Lightning protection is a requirement for all aircraft, particularly aircraft with composite structures. Due to its high strength to weight ratio, carbon fiber reinforced plastic (CFRP) material systems are increasingly used for aerospace structures. However, since carbon fiber is 2000 times more resistive than aluminum and is embedded in a matrix that typically consists of 35-40 weight % non-conductive contents, damage from direct lightning strikes to the CFRP structures is more severe and efforts to protect the CFRP structures from lightning direct attachment have required significant attention to ensure continued airworthiness of the design. Metallic skin fasteners, particularly fasteners in composite/non-metallic wing skins, require special attention as they are more susceptible to direct lightning attachment, if unprotected, and may lead to fuel tank ignition. Common approaches for lightning protection of fastened joints in the aerospace industry include minimizing lightning current entering the fastened joints, increasing the current carrying capacity of the fastened joints, containing energy released from the fastened joints, or some combination of these approaches. Various methods and technologies have been successfully implemented with proven lightning protection performance effectiveness. However, due to their complexity, these methods have often resulted in either high part costs, high manufacturing costs or high maintenance costs.
It is therefore desirable to provide less complex methods and designs for fastened joints in CFRP structures which maintain acceptable lightning protection at reduced costs.